Butterflies know where they are going. They might look indecisive as they flutter by, but British scientists now know better.

A team from Rothamsted Research in Hertfordshire fitted peacock butterflies and small tortoiseshells with radar backpacks and tracked their flightpaths.

The radar fitting must be one of the most intricate technological challenges ever attempted on wildlife. The delicate creatures had to be held down, given the lepidopterist's equivalent of a bikini wax and then fitted with transponders weighing just 12-thousandths of a gram. Researchers have used the same technique to track the flights of bees and bumblebees.

The insects could fly normally: the transponders weighed between 4% and 8% of their total bodyweight.

The scientists watched the butterflies play, feed and even mate. "It obviously didn't bother them that much," said Lizzie Cant of Rothamsted.

"Butterflies are good pollinators and I wanted to know whether or not they fly along linear features, along a fence row, or whether they can fly quite directly; whether from a distance they can see a patch and fly to it across the fields."